Simpson 64G988U

Not happy – We bought this house we are in 2 years ago and it was then 7 years old. The cooktop had a crack across one corner at the time of purchase and has since developed more larger cracks. We have been careful with it we feel. Also find the heat level very difficuilt as the elements don't reduce in heat when we turn them down. We have no way of knowing how the cooktop was looked after by previous owners. I have had a cooktop like this before and not had these problems so is this common or are we unlucky?

Regards Margaret